The (fictional, but intersecting with a number of real mathematicians) story of a woman trying to break into the very male world of mathematics. Although the mathematical theorems she discovers are (of course) fictional, they're described in vague enough terms that they stay plausible. The picture painted of academia is all too real at times, and occasionally depressing because of that (especially when you consider how entrenched some of those attitudes still are), but lifted up by Katherine's determination, and her love of the subject.